You already suspected that multiple hits to the head were bad for your kid’s health, but scientists at Boston Children’s Hospital just proved it.

Concussions are constantly in the news these days, and doctors and parents alike have long been concerned about the implications of kids having multiple head injuries. Boston Children’s Hospital has now confirmed those worries.

In a report published in the journal Pediatrics, Boston Children’s Hospital researchers say that kids who see doctors for a concussion take longer to heal if they have already had another concussion. Children who have a history of multiple concussions, or patients who have had at least one in the past year, were particularly at risk for prolonged symptoms after treatment. A report from USA Todayquotes the study’s author, Dr. Matthew Eisenberg:

“There may be a subgroup of kids, particularly those who play contact sports who are at risk over the course of their adolescence — those are the ones we worry about,” says Eisenberg, also an instructor in pediatrics at Harvard Medical School.

The researchersfollowed 280 individuals, all of whom were between the ages of 11 and 22 and arrived at the emergency department of Boston Children’s with acute concussions, for a year. Each patient’s recovery time and injury severity was assessed based on the Rivermead Pos-Concussion Symptoms Questionnaire, which asks patients about how they were injured, their medical history, and their symptoms. The survey was administered three months after the concussion, or until the patient’s symptoms—which usually include prolonged headache, confusion, dizziness, nausea, slurred speech, fatigue, and ringing in the ears—stopped.

Researchers found that the patients who had previously experienced concussions had a longer duration of symptoms than those who had never had a concussion. Patients who had experienced multiple concussions were susceptible to a longer recovery period than those who had experienced only one concussion within the previous year, but both groups still spent a few months recovering from the head injuries. A severe concussion—for example, if the patient lost consciousness because of the concussion—also caused prolonged recovery time.

So while most kids will recover from a concussion in a few weeks and studies like this are helping doctors better understand the nuances of concussion treatment, it’s clearer than ever than having multiple concussions is dangerous. And with more and more studies surfacing linking concussions to serious brain injury, the time for more research is now.

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